1. Field of the Invention
The invention relates to semiconductor light sources and semiconductor lasers.
2. Discussion of the Related Art
Materials with large second-order and/or third-order nonlinear susceptibilities can produce direct optical frequency-conversion. In direct optical frequency-conversion, incident light generates new light with a frequency that is the sum, difference, or a harmonic of the frequency or frequencies of the incident light. Thus, incident light at frequencies xcfx891 and xcfx892 produces light at one or more of the frequencies xcfx891+xcfx892, xcfx891xe2x88x92xcfx892, 2xcfx891, 2xcfx892, 3xcfx891, 3xcfx892, etc. Herein, the light produced by nonlinear processes at sums and differences of incident frequencies will be referred to as parametric light, and the light produced by nonlinear processes at doubles, triples, etc. of an incident frequency will be referred to as harmonic light.
Nonlinear optical materials have provided conventional sources for parametric and harmonic light. These conventional sources typically include one or more normal light sources, e.g., standard laser(s), and a non-linear crystal or a nonlinear optical fiber. The nonlinear crystal or nonlinear optical fiber generates parametric and/or harmonic light in response to receiving high intensity incident light from the normal light source(s). Such conventional sources for parametric and/or harmonic light are complex and need substantial optics for coupling the normal light source(s) to the nonlinear crystal or nonlinear optical fiber.
It would be advantageous to have a monolithic source for parametric and/or harmonic light, because such a source would require less optics for coupling the normal light source or sources to the nonlinear optical material.
Inter-intersubband transitions in multiple quantum well structures have produced optical frequency-conversion by nonlinear processes, but not in monolithic structures. Instead, the frequency conversion was produced by externally illuminating quantum well structures with intense light produced by physically separate mid-infrared lasers. Such coupling configurations are not geometrically optimal due to the in-plane nature of such inter-subband transitions.
The various embodiments provide monolithic semiconductor sources for parametric and/or harmonic light. In monolithic sources, lasing materials couple directly to the nonlinear medium for frequency-conversion without intervening optical couplers.
In one aspect, the invention features a monolithic apparatus having a laser cavity. The laser optical cavity has a multi-layer structure that includes a first active semiconductor multi-layer and a second semiconductor multi-layer. The second semiconductor multi-layer is located laterally adjacent to the first active semiconductor multi-layer. The first active semiconductor multi-layer includes a sequence of quantum well structures that produce light of a lasing frequency in response to being electrically pumped. The second semiconductor multi-layer includes a sequence of quantum well structures and is configured to both absorb light of the lasing frequency and produce one of parametric light and harmonic light in response to absorbing the light of the lasing frequency.
In another aspect, the invention features a monolithic apparatus that includes a laser optical cavity. The laser optical cavity has an active semiconductor multi-layer with a sequence of quantum well structures. The sequence of quantum well structures produces light of a lasing frequency in response to being electrically pumped. The sequence of quantum well structures is configured to absorb light at a harmonic of the lasing frequency and to produce light at the harmonic of the lasing frequency in response to the cavity lasing at the lasing frequency.